Titanium figures prominently in the manufacture of contemporary integrated circuits. Titanium is frequently reacted with silicon interconnect lines to reduce their sheet resistance. Titanium nitride, a hard gold-colored compound, is commonly used as a barrier material where both conductivity and resistance to ion migration are important. Titanium carbide, a good dielectric, may also be used as a barrier material in certain applications. A metallic titanium layer is often used as a "glue" layer to promote adhesion of subsequently deposited layers to an underlying layer. Titanium-containing layers are often formed by reacting other compounds with a titanium metal layer.
Heretofore, reactive sputtering was the only method available for depositing a titanium metal layer on a substrate. For deposition of titanium metal on a planar surface, reactive sputtering works reasonably well. However, step coverage on steeply sloped and vertical surfaces is poor. Given the fact that the trend in integrated circuit manufacturing is toward smaller dimensions and greater topography, the days of reactive sputtering as a deposition technique in integrated circuit manufacture are numbered.
Creating titanium metal layers on a substrate through chemical vapor deposition would be advantageous, as very thin layers having highly uniform thickness on both horizontal and vertical surfaces would be possible. Unfortunately, there are relatively few known titanium sources and no commercially available low-valent sources which might serve as a precursor for chemical vapor deposition. It is generally acknowledged that the lower the valence of the metal atom in a metal-organic precursor compound, the easier it is to reduce the metal in the compound to the zero valence state.